The overall objective of the research supported by this grant is to obtain increased knowledge about the opsonic activity of human serum and determine how this activity relates to host defense against bacterial, fungal or viral disease. Responsiveness of neutrophils from newborn infants that are healthy and from those that are compromised will be studied. Serum will be assayed for opsonic activity from these infants and from patients with increased susceptibility to infection and/or with recurrent infections. These sera will also be tested for factors which regulate chemotaxis of neutrophils. Studies of alternate pathway of complement activation components will be studied in our functional assay systems, and these findings will be correlated with quantitative data determined in collaboration with investigators in the renal group in the Pediatric Department at the University of Minnesota Medical School. Studies of the influence of factors such as antibiotics and catecholamines on serum opsonic and chemotactic activity and on neutrophil function will continue.